The invention is based on a priority application EP01440193.9.
The invention relates to a device and two methods for fixing an optical or electric cable against the inner wall of a pipe.
The use of waste-water, rain-water or mixed-water conduits or other discharge or supply lines for laying communications cables is one possible way, which has already been used, of reducing underground construction costs for the connection of subscribers (access). In addition, it makes possible to expand such connection of subscribers in a demand-orientated and rapid manner, something which has become increasingly important of late because of the large number of operators. In what follows, the term “waste-water conduit” (waste-water pipe) is also intended to cover rain-water conduits, mixed-water conduits and discharge or supply lines. Whereas it is possible, in case of accessible conduits, to employ the existing standard techniques for laying communications cables, the problems in case of inaccessible conduits are still unresolved to a very great extent.
When laying cables in inaccessible waste-water conduits (diameters of less than 20 cm), care has to be taken to ensure that                the hydraulically usable cross-sectional area is only slightly reduced;        as far as possible, no objects must be laid transversely to the direction of flow;        no points of attachment are produced which can lead to the formation of snags (for example, the accumulation of sewage materials) and consequently to obstruction; and        that cleaning of the waste-water conduit is not prevented.        
DE 198 26 880 discloses a device which consists of a plastic element which is annular in cross-section and which, as a result of a memory effect, enlarges its outer diameter when heat is supplied or as a result of moistening. This takes advantage of the reverse shrinkage effect. The device is compressed after shaping, and will expand after being reheated. This reheating then takes place in the waste-water conduit, so that the device rests against the inner wall of the waste-water conduit. The plastic element is introduced into the waste-water conduit in the pressed state, with an optical or electric cable. In the expanded state, the plastic element will fix the optical or electric cable against the inner wall of the waste-water conduit.
Plastics which have a pronounced memory effect consist of a relatively expensive material. In addition, this memory effect is inclined to decline gradually in the course of time. If these plastic elements are used in the form of a hose in order to simultaneously permit repair of the waste-water conduit, the usable clear space of the latter is then restricted to too great an extent. The result of this is that plastic elements of this kind do not represent an ideal solution for both fixing optical or electric cables and repairing the waste-water conduits.